Many passenger vehicles now incorporate an integrated communication system, such as a Mobile Vehicle Communication Units (MVCU), providing a variety of fee-based subscription services in a mobile environment including navigational assistance. The MVCU is typically a vehicle telematics device including a cellular radio, satellite transceiver, and/or global positioning capabilities. Typically, a radio communication link is established between the MVCU and a call center through a wireless network.
Off board navigation is a means of providing turn-by-turn directions with a navigation device that obtains a route from a remote source (i.e., transmitted to the MVCU from the call center via the wireless network). Routes are generated then transmitted as route guidance data to a navigation device. One form of route guidance data transmitted to a navigation device for off-board navigation is data derived from a digital map database limited to data representing only the route being traversed. No additional digital map database data representing the road network around the route is transmitted. This form of route guidance data requires a minimum amount of data to be transmitted, thus reducing data transmission time and cost. However, using this form of route guidance data, correcting off-route conditions requires that a new route be transmitted, since additional digital map database data is not resident in the navigation device to generate a new route. Off-route conditions are determined by monitoring when the vehicle is positioned beyond a threshold distance away from the transmitted route, as opposed to determining that the vehicle is traveling on a road that is not part of the route.
To avoid having to transmit a new route to correct off route conditions, digital map database data representing the road network around the route can be transmitted along with the route to enable the navigation device to recalculate either a new route or a route back to the original route. Typically, the digital map database transmitted along with the route is limited to a fixed distance corridor around the route. Transmitting the corridor of digital map database data around the route increases data transmission time and cost. It would be desirable to provide a strategy for minimizing the amount of data transmitted and to avoid having to transmit a new route to correct an off road condition.
It is an object of this invention, therefore, to provide a strategy for selecting route guidance data for off-board navigation, and to overcome the deficiencies and obstacles described above.